If you ever "purchased" (claimed for free) Mavericks in the past under your Apple ID, it is still in your account.
A DMG sitting on your desktop is useless if your Mac won't boot. You need to create a bootable USB drive (8GB minimum).
A DMG sitting on your desktop is useless if your Mac won't boot. You need to create a bootable USB drive (8GB minimum). mavericks os x 10.9.x dmg